121, 111211, 311221 Puzzle (Look and Say Sequence)

Date: 10/23/2001 at 22:28:06
From: Doctor Paul
Subject: Re: What's the next number?
The first number is 121. If you were to describe this number to
someone who was writing it down digit by digit, you would say:
Write down a single one - that is, one one. Then write down a single
two - that is, one two. Finally, write down a single one - that is,
one one.
Put them together: one one one two one one
Notice that this gives the next number: 111211
To describe this number in words digit by digit gives:
three ones, one two, two ones = 311221
A similar pattern shows that the next numbers in the sequence are:
13212211, 111312112221, 31131112213211
- Doctor Paul, The Math Forum
http://mathforum.org/dr.math/